1. Field of the Invention
The present invention generally relates to etch chambers. More particularly, the present invention relates to an insulator for a substrate support member in an etch chamber.
2. Background of the Related Art
As integrated circuit (IC) dimensions become increasingly smaller, the need to prevent contamination by particles of the substrates on which the IC's are constructed becomes increasingly more difficult and hence, more important, because the smaller circuits can be more easily damaged by smaller particles and the new processes required to construct the smaller circuits are more susceptible to degradation by the smaller particles. Thus, the need to keep the process and related hardware components clean is becoming more important.
In order to fabricate a complete IC, typically several substrate processing systems are used, with each system performing a particular step or series of steps in the overall fabrication process. The substrates are transferred between the systems at ambient conditions. The ambient environment is maintained very clean to prevent contamination of the substrates as they are transferred between systems. The substrates may even be transferred in completely enclosed cassettes in order to further prevent contamination thereof. A problem, however, is that it is not possible to prevent the oxygen in the ambient air from forming oxides on the surfaces of the substrates. Because the oxidation of the materials in an IC can seriously alter the electrical properties of the materials, oxidized surfaces are undesirable, and the surface oxides, primarily silicon dioxide and metal oxides, need to be removed or etched from the surfaces of the substrates, in a pre-processing cleaning step, before the substrates are subjected to the primary process of the system such as physical vapor deposition and chemical vapor deposition. Particularly, substrate surface features, such as trenches, contacts or vias into which metal conductors, such as tungsten, aluminum or copper, are to be deposited need to be cleaned in order to assure a very low interface resistance between layers of deposition.
A pre-clean chamber, such as the Pre-Clean II Chamber.TM. available from Applied Materials, Inc., Santa Clara, Calif., cleans the substrates by removing the undesired layer of oxides. FIG. 1 is a simplified schematic view of a pre-clean chamber. Generally, the pre-clean chamber 10 has a substrate support member 12 disposed in a chamber enclosure 14 under a quartz dome 16. The substrate support member 12 typically includes a central pedestal plate 18 disposed within a recess 20 on a quartz insulator plate 22. The upper surface of the central pedestal plate 18 typically extends above the upper surface of the quartz insulator plate 22. A gap 24 of about 0.035 inches is formed between a bottom surface of the substrate 26 and the top surface 23 of the quartz insulator plate 22. During processing, the substrate 26 is placed on the central pedestal plate 18 and contained thereon by locating pin 32. The peripheral portion of the substrate 26 extends over the quartz insulator plate 22 and overhangs the upper edge of the quartz insulator plate 22. A beveled portion 28 of the quartz insulator plate 22 is disposed partially below this overhanging peripheral portion of the substrate 26, and a lower annular flat surface 30 extends from the lower outer edge of the beveled portion 28. The quartz insulator plate 22 is typically a part of a process kit that system operators periodically replace during routine maintenance. It is desirable that a process kit has a long useful lifetime, so that the downtime of the system will be a small percentage of the overall processing time.
The primary purpose of the etch cleaning is to remove oxides that form on the surface of the substrate typically when the substrate was subjected to ambient air conditions while being transported to the vacuum processing system. For a silicon substrate, most of the oxidized surface material is silicon oxide, but metal deposited on the surface of the substrate will have formed metal oxides on the surface as well. The etched material sputters off the substrate surface and forms a film on the process kit, including the exposed surfaces of the quartz insulator plate. However, it is undesirable and unnecessary to sputter material from the backside of the substrate where the substrate overhangs the insulator plate because an excess of sputtered material is generated by the backside sputtering.
As the film forms on the process kit surfaces, its density may change, resulting in stress on the film. This stress, along with differences in the coefficients of expansion of the materials in the film, can result in delamination, or flaking, of the film from the surface of the process kit. Eventually, after several hundred substrates have been cleaned, the film becomes so thick and heavy that it starts to flake off and contaminate the substrate being processed. Because these particles can seriously damage the substrates and/or prevent the proper performance of the primary process of the system, the process kit is typically replaced after a certain number of substrates have been cleaned in the system. The selected number of substrates that can be processed before a process kit replacement generally corresponds to a permissible thickness of the film formed on the surfaces of the process kit before flaking occurs. It is desirable that the process kit has a long useful lifetime, so that the downtime of the system will be a small percentage of the overall processing time. Typically, the lifetime of a process kit is specified as a particular thickness of total etched material from the substrate because it is easier to measure the amount of material cumulatively etched off of the substrate surface than to measure the non-uniform film thickness on the process kit surfaces. The lifetime of a process kit varies according to the material being etched from the substrate. For example, the lifetime of the process kit for etching SiO.sub.2 typically is specified as 120 .mu.m of total etched material from the substrates, corresponding to about 3000 substrates. However, the actual lifetime for a process kit frequently falls short of the desired or specified lifetime because materials (other than the material specified as the lifetime of the process kit) are etched during the actual etching/cleaning process, and during actual process, a process kit may last for only 20-30 .mu.m of the cumulative etched material. These short lifetimes cause the system operator to have to service the system more often. Additionally, an unexpectedly short useful lifetime for a process kit may result in flakes of material falling onto a substrate, damaging many of the ICs formed on the substrate, while the system operator assumes that the process kit is working properly. Thus, several substrates may pass through the system before the system operator is aware that many of the devices are damaged or contaminated.
Therefore, there exists a need for an apparatus that minimizes backside sputtering of the substrate in a pre-clean chamber and other etch chambers. It would be desirable for the apparatus to reduce flaking of material from the film formed on the surfaces of the process kit. It would be further desirable for the apparatus to extend the specified lifetime of a process kit.